<!DOCTYPE html>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
iframe {
  position:absolute;
  top: 0px;
  left: 0px;
  width: 200px;
  height: 200px;
}

div {
  border-radius: 10px;
  position: absolute;
  top: 0px;
  left: 0px;
  width: 100px;
  height: 100px;
  background: blue;
}
</style>
<html>
<body>
<iframe src="/cross-site/bar.com/frame_tree/page_with_positioned_frame.html"></iframe>
<div></div>
</body>
</html>
